DOUBLE CRITICAL-STATE MODEL FOR THE WEAK-LINK REGIME OF GRANULAR HIGH-T-C SUPERCONDUCTORS

The phenomenological double critical-state model, which uses critical values for the components of the current-density both perpendicular an d parallel to the local magnetic induction B, is applied to tubes of g ranular high-T-c superconductors in the presence of axial and azimutha l magnetic fields. We develop a theory valid for the weak-link regime of these superconductors. In this theory not only intergranular but al so intragranular currents are taken into account. The behavior of the magnetic induction inside the wall of a superconducting tube cooled be low the critical temperature in the axial magnetic field and, later, s ubjected to an increasing azimuthal field, is analyzed. Our theoretica l results are compared with the experiment. (C) 1998 Elsevier Science B.V.